1. Field of the Invention
The present invention relates to a control for a vehicular powertrain comprising a fuel-controlled engine and a multiple-ratio drivetrain, including a multiple-speed transmission and a single- or mulitple-speed drive axle assembly. In particular, the present invention relates to a powertrain control wherein the maximum output torque of the engine is limited as a function of engaged drivetrain ratio.
2. Description of the Prior Art
Vehicular drivetrains including multiple-speed transmissions, usually compound transmissions, or simple transmissions coupled with multiple-speed axles, having 7, 9, 10, 13, 16, 18 or more forward speed ratios, are well known in the prior art, especially for heavy-duty vehicles, as may be seen by reference to U.S. Pat. Nos. 5,370,013; 5,527,237 and 4,754,665, the disclosures of which are incorporated herein by reference.
Control systems and methods for calculating engine output torque (also called xe2x80x9cflywheel torquexe2x80x9d) are known in the prior art, as may be seen by reference to U.S. Pat. No. 5,509,867, the disclosure of which is incorporated herein by reference.
Automated and manual transmission systems wherein engine output torque is controlled and/or limited as a function of engaged gear ratio and/or vehicle speed are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,477,827; 5,797,110; 5,457,633; 4,889,014; 5,738,606; 5,679,096 and 5,876,302, the disclosures of which are incorporated herein by reference. As is known, modern vehicular powertrains usually include electronically controlled engines, which may be controlled as to engine speed and/or engine torque. By way of example, according to the SAE J-1939 data link protocol, commands may be issued to the engine for fueling of the engine in accordance with (a) driver""s fuel demand, (b) a requested engine speed, (c) a requested engine torque and/or (d) a requested maximum engine torque and/or engine speed.
In accordance with the present invention, an improved control system/method for a vehicular powertrain is provided, which will tend to maximize vehicle performance while protecting the drivetrain from possible damage and/or undue wear caused by allowing excessive torque to be applied thereto under certain vehicle operating conditions. The foregoing is accomplished by limiting engine output torque to a first maximum value when the drivetrain is in a start ratio condition, by limiting engine output torque to a second maximum value when the drivetrain is in an intermediate ratio (the second maximum value being greater than the first maximum value), allowing engine torque to equal a third maximum value greater than the second maximum value when the transmission is in a direct drive or 1:1 ratio, and allowing engine torque to equal a fourth maximum value when the transmission is in an overdrive ratio condition (the fourth maximum value being less than the third maximum value but greater than the second maximum value).
Accordingly, it is an object of the present invention to provide a new and improved engine output torque control for a vehicular drivetrain system, preferably a vehicular powertrain system including a transmission having a direct drive ratio.